Dental x-ray machine

ABSTRACT

A dental x-ray machine for taking a panoramic x-ray of a patient&#39;&#39;s dental arch having located beneath the seat of the patient chair, the apparatus for rotating the x-ray source and film holder around the head of the patient. Also located below the chair seat is a cam controlled X-Y drive for driving the rotating x-ray source and film holder through a predetermined closed path of travel which, together with the rotation of the xray source produces a net movement that approximates the curve of the dental arch. The size of the pattern traced by the X-Y drive is continuously variable for adapting the pattern to dental arches of all sizes.

Ensslin et al.

[451 Sept. 16, 1975 Moss 250/320 x DENTAL X-RAY MACHINE 3,673,408 6/1972 [75] Inventors: a E i; izzig fi xv Yarnall Primary Examiner-Davis L. Willis Attorney, Agent, or Firm-Theodore B. Roessel; Roger [73] Assignee: Sybron Corporation, Rochester, Aceto 22 Filed: Sept. 9, 1974 [57] ABSTRACT A dental x-ray machine for taking a panoramic x-ray [211 App! 504274 of a patients dental arch having located beneath the seat of the patient chair, the apparatus for rotating the 52 us. (:1. 250/320; 250/444; 250/521; y Source and film holder around the head of the 250 523 patient. Also located below the chair seat is a cam 51 Im. cl. G03B 5/17 controlled X Y drive for driving the rotating y [58] Field of Search 250/320, 323, 439, 444, source and film holder through a predetermined 250/445, 446, 447, 454, 456, 475, 478, 479, Closed path of travel which, together with the rotation 490 52 522 523 52 5 of the x-ray source produces a net movement that approximates the curve of the dental arch. The size of [56] R f en Cited the pattern traced by the X-Y drive is continuously UNITED STATES PATENTS variable for adapting the pattern to dental arches of all 2,798,958 7/l957 Hudson et al 250/523 X Slzesi 3,536,913 lO/l970 Huchel 250/320 X 18 Claims, 7 Drawing Figures It I l fl 2o T\ 22 L l7 l5 PATENTEB SEP I 6 I975 sum 2 qg 4 N GE PMENIEBSEP 18 E975 SHEET 3 BF 4 PATENTEB SEP 1 6 I975 SHEU '4 BF 4 FIG. 6

DENTAL X-RAY MACHINE BACKGROUND OF THE INVENTION The present invention relates generally to a dental x-ray machine for taking a panoramic or full mouth x-ray of the patients teeth. More specifically, the present invention relates to a dental x-ray for taking full mouth x-rays by rotating the x-ray source and x-ray film about the head of the patient through a path of travel which closely approximates the shape of the dental arch.

Various techniques and apparatus for taking a full mouth x-ray are well known in the art. When taking a full mouth x-ray, it is important that the x-ray source and film be moved about the head of the patient through a path of travel which closely parallels the dental arch with the depth of focus between the x-ray source and film following along a path on the dental arch. In this way, only the particular tooth being radiographed remains in focus. The difficulty is that the dental arch is not easily approximated so that systems of the prior art only generally followed the dental arch by rotation around a double or triple center of rotation or utilized and eIlipsograph-type drive to move the x-ray source and film around the outline of an ellipse. Other systems required that the patient be moved laterally in order to change the center of rotation or stepped the drive through several centers of rotation in an attempt to approximate the shape of the dental arch.

The size of the dental arch varies from patient to patient and with the exception of the ellipsograph type drive, the apparatus of the prior art could only adjust the pattern size in very coarse steps requiring considerable effort on the part of the operator.

Prior art panoramic x-ray machines also located the drive mechanism as well as the high voltage power sup ply for the x-ray source above the head of the patient. This required relatively massive support columns and in some cases the structure had to be wall mounted to prevent toppling of the top heavy apparatus. Wall mounting is also necessary in order to dampen any vibration produced by the drive as such vibrations will reduce the quality of the x-ray picture. Vibrations are caused, in particular, by drives of the prior art in which the mechanism is stepped from one center of rotation to another.

The x-ray of the present invention overcomes the drawbacks of the prior art by locating an X-Y drive mechanism and the high voltage power supply in the base of the apparatus beneath the seat of the patient chair thus avoiding any massive overhead structure and the need for wall mounting. The X-Y drive mechanism is controlled by a cam which produces a smooth motion and this motion, when coupled with rotation of the x-ray source and film holder about the head of the patient, produces a net movement which allows the focal plane between the x-ray source and film to follow along the shape of the dental arch. The cam drive also allows the size of the pattern to be quickly and easily changed in an infinite number of steps over the entire adjustment range.

Another feature of the present invention is an automatic apex adjustment which displaces the x-ray axis of rotation towards or away from a fixed reference point whenever the pattern size is respectively decreased or increased. This allows positioning both the addult and child patient at the same fixed reference point correspending to the front of the patients mouth so that the x-ray source and film holder will be properly oriented to the patient regardless of his or her size.

SUMMARY OF THE INVENTION The present invention may be characterized in one aspect thereof by the provisions of a fixed base supporting a patient chair; a platform carried on the base beneath the seat of the patient chair and supported for movement through a closed path of travel in an x-y plane; a column upstanding from the platform and rotatable about a vertical axis, the upper portion of the column supporting the x-ray source and a film holder for movement about the head of the patient; and means on the platform cooperating with the fixed base for both rotating the column and moving the platform along a closed curved path of travel in an x-y plane, the rotation of the column and the movement of the platform together producing a net movement of the x-ray source and a film holder along the path of travel which closely parallels the dental arch of the patient seated in a chair.

OBJECTS OF THE INVENTION One object of the present invention is to provide a dental x-ray apparatus for taking a full mouth x-ray, including the mandibular joints, in which the motion of the x-ray source and film holder about the head of the patient closely follows along a path paralleling the shape of the patients dental arch.

Another object of the present invention is to provide a dental x-ray apparatus wherein the size of the pattern followed by the x-ray source and film holder about the head of the patient is quickly and easily adjusted.

A further object is to provide a panoramic dental x-ray apparatus wherein the means for controlling the rotation of the x-ray source and film holder about the head of the patient as well as the means for moving the axis of rotation is located in the base of the apparatus beneath of the seal of the patient chair.

Still another object is to provide a panoramic dental x-ray system wherein the high voltage power supply for the x-ray source is located in the base of the apparatus, the power supply being cable connected to the x-ray source located at a distance from the power supply.

Yet another object is to provide a panoramic dental x-ray machine which is a self contained unit requiring no installation or wall supports.

A still further object of the present invention is to provide an x-y drive for a dental x-ray having an automatic apex adjustment which shifts the x-ray axis of rotation as the size of the pattern traversed by the x-ray source and film is changed.

These and other objects, advantages and characterizing feature of the present invention will become more apparent upon consideration of the following detailed description thereof when taken in connection with the accompanying drawings depicting the same.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view showing the dental x-ray apparatus of the present invention;

FIG. 2 is a front elevation view of the apparatus base, partly away and in section, showing the X-Y drive on an enlarged scale;

FIG. 3 is a plan view of the X-Y drive with portions removed for clarity;

FIG. 4 is an elevation view on an enlarged scale of a ortion of the Y-reaction arm of the drive;

FIG. 5 is a view similar to FIG. 3 with still further porions removed for clarity to show the X-reaction arm nd apex adjustment mechanism;

FIG. 6 is an elevation on an enlarged scale of an apex ompensating mechanism associated with the X- eaction arm; and

FIG. 7 is a plot showing the XY drive path of travel nd the net movement generated by the apparatus Ihen taking an x-ray of a large and a small detal arch.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, FIG. 1 shows the x-ray aparatus of the present invention generally indicated at 0. The apparatus includes a supporting base 12, a pa- .ent chair 14 carried by the base, and a column 16 uplanding from the base and supported for rotation bout a vertical axis passing generally through the seat f the patient chair. Column 16 is generally L-shaped 'herein the horizontally deposed leg 17 passes beneath 1e seat of the chair. At the top of column 16 is an x-ray Jurce l8 and an x-ray film cassette 20. The cassette is .ipported on a curved outwardly extending horizontal rm 22, so that the patient to be x-rayed can be posioned between the x-ray source and the film cassette. he upright structure indicated at 24 at the front of the ental chair and the chin and forehead rests 26, 28 repectively are used for properly positioning the patient. should be appreciated, that the chin and forehead :sts define a fixed reference point for properly posioning the head of the patient for the x-ray procedure. 1 order to bring patients of different sizes to this refernce point, chair 14 can be raised or lowered and the ackrest 30 moved on ways 32 front-to-back of the hair.

A transformer 13 and other electrical components )r activating the x-ray source are located within base 2 at any convenient location, preferably at a rear poron thereof. A flexible electrical cable extends cm the transformer and passes up through column 16 ncluding leg 17) for connecting the power supply to re x-ray source.

Disposed within base 12 is the means for rotating the )lumn about its vertical axis and for moving the axis frotation through a closed path of travel in the XY lane. As shown in FIG. 2, base 12 is generally U- raped in cross-section having a horizontal base leg 34 id upstanding sides 36 a and b. The base or horizontal g 34 is adapted to rest on a floor surface and is proded with a pair of spaced parallel ways 38 which are fiented along the X axis of the base, that is, front-toick. Slidably carried on these ways is a carriage 40. Carriage 40 is also U-shaped in cross-section having base 42 and upstanding front and rear wall members I, only the rear one of which is shown in FIG. 2. The irriage in turn, carries adjacent the upper end of each all 44 a pair of parallel ways 46. Ways 46 are oriented )rmal to ways 38 and are aligned generally along the -axis of base 12 or side-to-side. Slidably carried on ays 46 is a platform 48. Due to the orientation of ways I and 46, it should be apparent that platform 48 can moved along both the X and Y axis of base 12. Suspended from platform 48 are a plurality of colnns 50 which in turn support a plate 52 in spaced relationship from platform 48. Disposed between the platform and the plate and carried in part by the plate are the various mechanisms for driving the platform through a closed path of travel in the XY plane.

As shown in FIG. 2, an upright shaft 54 is supported by and is journaled to platform 48 and plate 52 by means of bearings 51, 53 respectively. With this arrangement, the shaft is free to rotate about its vertical axis while the axis is being transported through a closed path of travel in the XY plane. It should be appreciated that the horizontal leg 17 of column 16 is fixed at one end to the portion 56 of the shaft located above platform 48. The portion 58 of the shaft located between platform 48 and plate 52 is fixed to a cam member 60.

The cam is generally disc-shaped having endless grooves 62 and 64 cut into the top and bottom surfaces respectively of the disc. These grooves comprise the cam surfaces for programming the motions of the platform as further set out herein below.

A drive motor 66 fixed to plate 52 rotates the cam and therefore, shaft 54 by means of a drive belt 68 which engages around the periphery of the cam. v In order to translate the movement of cam surfaces 62, 64 into motion of platform 48 through a closed path of travel in the XY plane, a cam follower is associated with each of the cam grooves. In this respect, cam groove 62 and its associated cam follower cooperate to move platform 48 through the Y component of travel (side-to-side) whereas cam groove 64 and its associated cam follower cooperate to move platform 48 through the X component of travel (front-to-back). The net result is movement of platform 48 through a closed path of travel in the XY plane.

CONTROL OF Y COMPONENT Referring to FIGS. 2, 3 and 4 the cam follower associated with groove 62 includes a horizontal pick-off arm 70, which is journaled at one end 72 to platform 48 by means of a vertical shaft 74 extending between the platform and plate 52 (FIG. 2). Fixed to pick-off arm at a given point along the arm is a cam follower 76, best seen in FIG. 4, which rides in cam groove 62. The distance between cam follower 76 and shaft 74 is a fixed dimension and as the cam rotates under the fixed cam follower, the pick-off arm rocks about its journaled end 72 depending upon the radial distance of the cam groove from shaft 54.

As shown in FIGS. 3 and 4, pick-off arm 70 is provided with a lead screw 78 which drives a nut 80 along the arm to increase or decrease respectively the linear distance of the nut from shaft 74. Upstanding from nut 80 is a pin 82 which is in turn, journaled to one end of a rigid reaction arm 84. The other end of reaction arm 84 is slidably mounted on a way 86 carried at the top of upstanding base side 36a, way 86 being alligned generally parallel to ways 38 (FIGS. 2 and 3).

With this arrangement, reaction arm 84 is free to move along the Xaxis of the base, but is fixed against movement in the Y direction. Thus, as cam disc 60 is rotated and the radial distance of cam groove 62 changes with respect to shaft 54, the reaction arm will force platform 48 to move to the left or the right as viewed in FIGS. 2 and 3. For example, as the radial distance of cam groove 62 from shaft 54 increases, the entire mechanism supported by platform 48 will shift to the left as viewed in FIG. 3 and conversely, will shift to the right as viewed in FIG. 3 when the radial distance CONTROL OF X COMPONENT A somewhat similar arrangement is provided for translating the rotational movement of cam groove 64 into movement of platform 48 along the X axis of base 12. In this respect, FIG. 5 is a plan view of the XY mechanism similar to FIG. 3 only with some parts removed for clarity, such as pickoff arm 70, reaction arm 84 and portions of cam disc 60.

FIG. 5 shows a second, generally L-shaped pick-off arm 88 having legs 90 and 92. At one end of the pickoff arm (leg 90) is a cam follower 94 which extends up into cam groove 64 cut into the bottom surface of cam disc 60. Pick-off arm 88 is also journaled intermediate its ends to vertical shaft 74 so that the distance from the shaft to cam follower 94 is a fixed distance. The other leg 92 of the L-shaped pick-off arm carriesa lead screw 96 which in turn drives a nut 98 (FIG. 3). The adjustment of this nut along leg 92 accomplishes a result similar to the adjustment of nut 80 along pick-off arm 70. In other words, such movement will either scale up or down the effect of a throw of cam groove 64 depending upon whether the nut is moved respectively away from or towards shaft 74.

Extending horizontally from upstanding side 36b of the base is a fixed member 100 only a portion of which is shown in FIG. 5. Since this member is fixed to side 36b, it represents a ground station. A way 102 is carried on member 100, the way being oriented generally parallel to ways 46 and normal to ways 38 (FIGS. 2 and 3). Slidably carried on way 102 is an apex adjustment means generally indicated at 104. While this means will be described more fully herein below, it is sufficient for the present merely to say that the apex adjustment means 104 is also pinned to nut 98 so that it is similar in one aspect to reaction arm 84. That is, means 104 is free to slide with the X-Y drive mechanism in either direction along the Y axis of base 12, but it is fixed by member 100 against movement in the X direction. Thus, any variation in the radial distance of cam groove 64 from shaft 54 is translated into movement of platform 48 in the X direction. For example, as the radial distance decreases, the L-shaped pick-off arm 88 will rock clockwise about shaft 74 causing the platform 48 to shift toward the top of the Figure as view in FIGS. 3 and 5 which is towards the back of the apparatus. Conversely, any increase in the radial distance of the cam groove 64 from shaft 54 will cause the L-shaped arm to rock counter-clockwise about shaft 74 causing the platform to shift direction towards the bottom of the Figure as view FIGS. 3 and 5 which is toward the front of the apparatus.

Thus, the mechanism described herein above cooperates in response to rotation of cam disc 60 to move platform 48 and therefore, the axis of rotation of column 16 in a closed path of travel in the X-Y plane. As column 16 is connected to shaft 54, rotation of cam 60 will likewise, rotate the column. For example, the path of travel generated by the X-Y drive is shown in FIG. 7 at 130. Only one halfthe curve is shown and it should be understood that the missing portion is a mirror image of that shown. It should be appreciated that reference 130 represents the path of travel of shaft 54 and therefore, the axis of rotation of column 16. The curve 132 in heavy solid line represents a locus of points within the depth of focus and includes both the mandibular joints and the dental arch. Points 1-8 represent various positions of the x-ray film during the x-ray procedure and are along a path generally parallel to the dental arch. The position of the x-ray source, while not shown is understood to be on the far side of the axis of rotation from points l-8. From FIG. 7, it should be apparent that the rotational movement of the column, when associated with the movement in the X-Y plane of platform 48 from which the column upstands, produces a net movement of the x-ray source 18 and film cassette 20 along a path of travel which parallels the dental arch. As shown by heavy solid line 132 in FIG. 7, the x-ray is taken starting at the left mantibular joint L,. It then moves inward to x-ray the last molar L on the left side and then along the dental arch to the last molar R on the right side of the mouth and then outward to x-ray the right mandibular joint R CHANGE OF X-Y PATTERN SIZE As previously stated, the size of the pattern traveled by the platform can be changed by moving the points of the pick-offs defined by nuts and 98. This is accomplished by the simultaneous rotation of lead screws 78 and 96 to move the nuts toward or away from shaft 74. For this purpose, a second drive motor 106 is mounted on plate 52 (FIGS. 3 and 5). When actuated, this motor drives both lead screws through a system of bevel gears 108. Actuation of the motor can be accomplished by any suitable means (not shown) such as a hand controller. It should be appreciated that such an arrangement allows an infinite adjustment of the pattern size within the full limits of the adjustment range.

As the pattern size is adjusted, it is important that a common reference point be maintained for all pattern sizes. Preferably, this common point is located at the front of the dental arch, as defined, for example, by the chin and head rests 26, 28 respectfully, at the front of the dental chair which are used for properly positioning the patient. For example, FIG. 7 shows at a path of travel as may be generated by the mechanism for making a full mouth dental x-ray of the derital arch of an adult. Reference 130a line shows a smaller, symmetrical, pattern of the path generated for making an x-ray of a younger person whose dental arch is included in the light solid line curve shown at 132A. The point indicated at A is common to both patterns and is located at the front or apex of the dental arch. Thus, when the size of the pattern is changed, it is necessary to provide an adjustment which maintains the position of point A. This is accomplished by an apex adjuster which shifts the XY path of travel towards point A when a child is in the chair and away from point A when a adult is in the chair.

APEX ADJUSTMENT The apex adjuster generally indicated at 104 can be seen in plan view in FIGS. 3 and 5, and in elevation view in FIGS. 2 and 6. As described hereinabove, there is a way 102 mounted on member 100, which in turn is attached to the ground of the apparatus. Also as previous stated, way 102 is oriented parallel to ways 46 d normal to way 38 (FIG. 3). Slidably mounted on 1y 102 is a block 110. The ends 112 of the block IG. 6) are mitered and slidably fit into a pair of horintal side supports 114. Supports 1 14 extend in canti- I81 fashion from a mounting bracket 116 which pnds from platform 48 (FIGS. 2 and 3). With the arngement described thus far, it should be appreciated at block 110 is free to slide with platform 48 in the direction of the chair, but that the block, being on ly 102, is fixed from sliding in the X direction. Hower, due to the sliding relationship between block 110 d side supports 114, the supports and platform 48 n slide with respect to the block in the X direction. To accomplish the apex adjustment, which requires Jvement in the X direction or front-to-back, FIGS. 5 d 6 show that block 110 contains a diagonal cam oove 118 which slidably retains a follower 120. The llower depends from nut 98 and is therefore tied, via g 92 and shaft 74, to platform 48 with the screw pertting an adjustment of the nut with respect to the itform. Cam groove 118 is oriented generally on the agonal of block 110 to accomplish the apex adjustam as set out hereinbelow. As previously stated, rotating screw 96 to move nut with respect to platform 48 to the left or the right viewed in the Figures, will respectively increase or crease the size of the X component at the pattern. ovement of the nut will in turn drive follower 120 ainst one side or the other of inclined slot 118. The essure of follower 120 against the side of slot 118 nnot be relieved by a corresponding movement of itfOIIT] 48 in the Y direction as movement in the Y rection is prevented by reaction arm 84. Conseently, such pressure is relieved by follower 120 ridg up or down the inclined slot as viewed in FIGS. 3 d 5. As follower 120 is tied to platform 48, move- :nt of the follower in the X direction produces a like )vement of platform 48, wherein the platform, acket 116 and side supports 114 slide over block 110 the X direction. By way of example, if nut 98 is moved to the left, as :wed in the Figures, to increase the size of the pat- 'n, follower 120 will be forced up the inclined slot 8 (FIGS. 3 and 5) moving platform 48 towards the ck of the apparatus and away from the reference deed by chin and head rests 26, 28 respectfully. If the t moves in the opposite direction to decrease the pat- 'n size, follower 120 will be forced down the inclined It moving platform 48 towards the reference point fined by the chin and headrests. Such movement wards and away from the chin and headrests mainns the key position of the apex of the pattern at point (FIG; 7) as the pattern size is changed. Thus, it should be appreciated that the present invenn accomplishes its present objects in providing a ntal x-ray apparatus for taking full mouth x-rays llCll is a self-contained unit requiring no installation wall support. The apparatus has the capability of iking an infinite adjustment of the size of the pattern lowed by the x-ray source and the film holder about 2 head of the patient. Such change in the pattern size accomplished quickly and easily while maintaining a mmon reference point with respect to all of the pat- 'n sizes. The majority of the weight of the apparatus, ldC up by the transformer and other electrical comnents and the XY drive mechanism, is located in base of the apparatus, so the apparatus can be made free standing and there is no need to wall supports for mounting the apparatus.

Since the present invention concerns primarily the general arrangement of the x-ray apparatus together with X-Y drive and apex adjustment as described herein, no mention is made of other features wellknown in the art which are essential to the operation of a pantographic dental x-ray machine of the type described. For example, it is well-known that as column 16 is rotated about a patient, means must be provided to accomplish an independent rotation of x-ray film cassette 20 in order to achieve proper exposure of the x-ray film. The rotation must be in a particular time sequence with the movement of arm 16, but as such a mechanism forms no part of the present invention, none has been described herein and the apparatus to accomplish this has been omitted from the drawing for purposes of simplification.

Having thus, described the invention in detail, what is claimed as new, is:

1. Dental X-ray apparatus of the type for taking a full mouth X-ray comprising:

a. a base adapted to rest on a floor surface;

b. a patient chair on said base and means for holding the head of the patient at a defined reference point;

c. platform supported for movement relative to said base in a X-Y plane beneath the seat of said patient chair:

d. a generally L-shaped column having a horizontal leg extending beneath said seat with one end of said leg being mounted to said platform for rotation about a vertical axis passing generally through the seat of said patient chair, the upstanding portion of said column extending to a point above said patient chair;

e. a horizontal arm extending outward from said column over said patient chair;

f. an X-ray source in said column and an X-ray film holder on the outward end of said horizontal arm in line with said X-ray source;

g. a power supply in said base connected to said X-ray source by flexible cable means extending through said column;

h. first drive means carried by said platform for rotating said column and therefore said X-ray source and film holder about said vertical axis, whereby said X-ray source and film holder orbit the head of a patient positioned at said reference point; and

i. second X-Y drive means carried by said platform and cooperating with said base for moving said platform uninterruptedly along a closed curved path of travel in an X-Y plane, which movement when associated with the rotation of said column produces a net orbital movement of said X-ray source and film holder along a path of travel which parallels the dental arch.

2. X-ray apparatus as in claim 1 comprising a carriage mounted for movement along a first axis of said base, said platform being mounted on said carriage for movement along a second axis of said base.

3. X-ray apparatus as in claim 1 wherein said second X-Y drive means comprises:

a. a rotatable cam member journaled to said platform;

b. first force transmitting means engaging said cam freely movable along a first axis of said base and fixed with respect to a second axis of said base for moving said platform along said second axis of said base responsive to the rotation of said cam; and

c. second force transmitting means engaging said cam freely movable along said second axis and fixed with respect to said first axis of said base for moving said platform along said first axis of said base responsive to the rotation of said cam.

4. X-ray apparatus as in claim 3 wherein said cam is disc-shaped having a cam surface in each face thereof, each of said force transmitting means including a cam follower engaging one of said cam surfaces.

5. X-ray apparatus as in claim 4 wherein said cam surfaces are formed by an endless groove in each face of said cam, each groove defining a motion component along a axis of said base.

6. X-ray apparatus as in claim 3 including a vertical shaft journaled to and extending through said platform, the portion of said shaft above said platform being connected to and forming the vertical axis of rotation of said column and the portion of said shaft below said platform mounting and forming the axis of rotation of said cam.

7. Xray apparatus as in claim 3 wherein said first and second force transmitting means are simultaneously adjustable for changing the size but not the shape of said closed curved path of travel through which said platform is moved.

8. Apparatus as set forth in claim 7 including apex adjustment means for shifting the axis of rotation of said shaft towards or away from said defined reference point as the shape of said closed path of travel is respectively decreased and increased.

9. X-ray apparatus as in claim 3 wherein said first force transmitting means comprises:

a. a shaft depending from said platform;

b. a first pick-off arm having one end journaled to said shaft;

c. a cam follower on said pick-off arm engaged with said cam;

d. a rigid reaction arm connected to said pick-off arm, said reaction arm being freely movable along an X axis of said base and fixed against movement along a Y axis of said base.

10. X-ray apparatus as in claim 9 wherein said second force transmitting means comprises;

a. a L-shaped pick-off arm journaled intermediate its ends to said shaft;

b. a second cam follower on one leg of said L-shaped pick-off arm engaged with said cam; and

c. a second reaction arm connected to the second leg of said L-shaped pick-off arm, said second reaction arm being freely movable along a Y axis of said base and fixed against movement along an X axis of said base.

11. X-ray apparatus as in claim 10 including:

a. a lead screw on said first pick-off arm and on the second leg of said L-shaped pick-off arm;

b. a nut driven by each screw along said arms towards and away from said shaft;

c. said reaction arms being connected to the nut on their respective pick-off arms; and

d. means for simultaneously rotating said screws to drive said nuts in concert toward or away from said shaft to vary the nut-cam follower distance and change the effect of the throw of said cam.

12. X-ray apparatus as in claim 1] including:

a. a way oriented parallel to the second leg of said L- shaped pick-off arm;

b. a block slidably mounted on said way;

0. a mounting bracket depending from said platform;

d. a pair of side supports extending from said bracket and slidably engaging said block, said side supports permitting movement of said platfrom over said block in a direction normal to said way and said way permitting movement of said block and platform in a direction parallel to said way; and

e. means connecting said block and the nut on the second leg of said L-shaped pick-off arm for moving said platform over said block as said nut is moved to change the throw of said cam.

13. X-ray apparatus as in claim 12 wherein said block has a generally diagonal cam groove therein and said means connecting said block and nut includes a follower connected to said nut and riding in said cam groove.

14. Dental X-ray apparatus of the type for taking a full mouth X-ray by orbiting an X-ray source and X-ray film holder about the head of a patient along an orbital path which follows the shape of the patients dental arch, and apparatus comprising:

a. a fixed base supporting a patient chair;

b. a platform movable with respect to said base and chair through a closed path of travel in an X-Y plane beneath said chair;

c. a column upstanding from said platform supporting said X-ray source and X-ray film holder, said column being rotatable about a vertical axis of rotation while being transported through said closed path of travel by said platform such that said X-ray source and X-ray film holder are orbited about the head of a patient through an orbital path which parallels the shape of the dental arch; and

d. X-Y drive means carried by said platform and cooperating with said base for moving said platform with respect to said base through said closed path of travel, said X-Y drive means including a rotatable cam carried by said platform and a pair of reaction arms extending between said cam and base, each of said reaction arms being freely movable with respect to said base along one axis thereof and fixed with respect to said base along another axis thereof, the throw of said cam during the rotation thereof forcing said reaction arms to move said cam and therefore said platform with respect to said base through said closed path of travel.

15. X-ray apparatus as set forth in claim 14 wherein said cam is disc-shaped having an endless cam groove in both the top and bottom surfaces thereof defining respectively the X and Y components of motion of said platform, and each of said reaction arms being associated with a cam follower engaged in one of said cam grooves. v

16. X-ray apparatus as in claim 15 including a vertical shaft depending from said platform, said X-Y drive means including:

a. a pick-off arm having one end journaled to said shaft, one of said cam followers being fixed to said arm;

b. a lead screw and nut on said pick-off arm, said screw being rotated for driving said nut along said pick-off arm towards and away from said shaft; and

c. one of said reaction arms being journaled at one end of said nut, the movement of said nut towards and away from said shaft acting to decrease and increase respectively the throw of said cam.

17. X-ray apparatus as in claim 15 including a vertial shaft depending from said platform, said X-Y drive leans including:

a. an L-shaped pick-off arm journaled intermediate its ends to said shaft, one of said cam followers being fixed on one leg of said L-shaped pick-off arm;

b. a led screw and nut on said second leg of said L- shaped pick-off arm, the rotation of said led screw driving said nut along said leg towards and away from said shaft;

c. a pin on said nut; and

d. means including one of said reaction arms journaled to said pin, the movement of'said nut towards and away from said shaft acting to decrease and increase respectively the throw of said cam.

18. Dental X-ray apparatus of the type for taking a ll mouth X-ray comprising:

a. a base adapted to rest on a floor surface;

b. a patient support means on said base including means for holding the head of a patient at a reference point;

e. a platform supported on said base for movement relative to said base'through a closed path of travel in an X-Y plane beneath said patient support means;

d. an X-ray source and film holder, said source and film holder being spaced and in line and rotatable about a vertical axis upstanding from said platform so as to orbit the head of a patient held at said reference point;

e. means for moving said platform through said closed path of travel while rotating said X-ray source and film holder about said vertical axis, the rotational movement of said X-ray source and film holder together with the movement of said vertical axis producing a net movement of said X-ray source and film holder along a path of travel which parallels the dental arch ofa patients head held at said reference point;

f. means for symmetrically changing the size of said closed path of travel; and

g. means for translating said platform towards and away from said reference point as the size of said path of travel is respectively decrease and increased. 

1. Dental X-ray apparatus of the type for taking a full mouth Xray comprising: a. a base adapted to rest on a floor surface; b. a patient chair on said base and means for holding the head of the patient at a defined reference point; c. platform supported for movement relative to said base in a XY plane beneath the seat of said patient chair: d. a generally L-shaped column having a horizontal leg extending beneath said seat with one end of said leg being mounted to said platform for rotation about a vertical axis passing generally through the seat of said patient chair, the upstanding portion of said column extending to a point above said patient chair; e. a horizontal arm extending outward from said column over said patient chair; f. an X-ray source in said column and an X-ray film holder on the outward end of said horizontal arm in line with said X-ray source; g. a power supply in said base connected to said X-ray source by flexible cable means extending through said column; h. first drive means carried by said platform for rotating said column and therefore said X-ray source and film holder about said vertical axis, whereby said X-ray source and film holder orbit the head of a patient positioned at said reference point; and i. second X-Y drive means carried by said platform and cooperating with said base for moving said platform uninterruptedly along a closed curved path of travel in an X-Y plane, which movement when associated with the rotation of said column produces a net orbital movement of said X-ray source and film holder along a path of travel which parallels the dental arch.
 2. X-ray apparatus as in claim 1 comprising a carriage mounted for movement along a first axis of said base, said platfoRm being mounted on said carriage for movement along a second axis of said base.
 3. X-ray apparatus as in claim 1 wherein said second X-Y drive means comprises: a. a rotatable cam member journaled to said platform; b. first force transmitting means engaging said cam freely movable along a first axis of said base and fixed with respect to a second axis of said base for moving said platform along said second axis of said base responsive to the rotation of said cam; and c. second force transmitting means engaging said cam freely movable along said second axis and fixed with respect to said first axis of said base for moving said platform along said first axis of said base responsive to the rotation of said cam.
 4. X-ray apparatus as in claim 3 wherein said cam is disc-shaped having a cam surface in each face thereof, each of said force transmitting means including a cam follower engaging one of said cam surfaces.
 5. X-ray apparatus as in claim 4 wherein said cam surfaces are formed by an endless groove in each face of said cam, each groove defining a motion component along a axis of said base.
 6. X-ray apparatus as in claim 3 including a vertical shaft journaled to and extending through said platform, the portion of said shaft above said platform being connected to and forming the vertical axis of rotation of said column and the portion of said shaft below said platform mounting and forming the axis of rotation of said cam.
 7. X-ray apparatus as in claim 3 wherein said first and second force transmitting means are simultaneously adjustable for changing the size but not the shape of said closed curved path of travel through which said platform is moved.
 8. Apparatus as set forth in claim 7 including apex adjustment means for shifting the axis of rotation of said shaft towards or away from said defined reference point as the shape of said closed path of travel is respectively decreased and increased.
 9. X-ray apparatus as in claim 3 wherein said first force transmitting means comprises: a. a shaft depending from said platform; b. a first pick-off arm having one end journaled to said shaft; c. a cam follower on said pick-off arm engaged with said cam; d. a rigid reaction arm connected to said pick-off arm, said reaction arm being freely movable along an X axis of said base and fixed against movement along a Y axis of said base.
 10. X-ray apparatus as in claim 9 wherein said second force transmitting means comprises: a. a L-shaped pick-off arm journaled intermediate its ends to said shaft; b. a second cam follower on one leg of said L-shaped pick-off arm engaged with said cam; and c. a second reaction arm connected to the second leg of said L-shaped pick-off arm, said second reaction arm being freely movable along a Y axis of said base and fixed against movement along an X axis of said base.
 11. X-ray apparatus as in claim 10 including: a. a lead screw on said first pick-off arm and on the second leg of said L-shaped pick-off arm; b. a nut driven by each screw along said arms towards and away from said shaft; c. said reaction arms being connected to the nut on their respective pick-off arms; and d. means for simultaneously rotating said screws to drive said nuts in concert toward or away from said shaft to vary the nut-cam follower distance and change the effect of the throw of said cam.
 12. X-ray apparatus as in claim 11 including: a. a way oriented parallel to the second leg of said L-shaped pick-off arm; b. a block slidably mounted on said way; c. a mounting bracket depending from said platform; d. a pair of side supports extending from said bracket and slidably engaging said block, said side supports permitting movement of said platfrom over said block in a direction normal to said way and said way permitting movement of said block and platform in a direction parallel to said way; and e. means connecting said block and the nut on thE second leg of said L-shaped pick-off arm for moving said platform over said block as said nut is moved to change the throw of said cam.
 13. X-ray apparatus as in claim 12 wherein said block has a generally diagonal cam groove therein and said means connecting said block and nut includes a follower connected to said nut and riding in said cam groove.
 14. Dental X-ray apparatus of the type for taking a full mouth X-ray by orbiting an X-ray source and X-ray film holder about the head of a patient along an orbital path which follows the shape of the patient''s dental arch, and apparatus comprising: a. a fixed base supporting a patient chair; b. a platform movable with respect to said base and chair through a closed path of travel in an X-Y plane beneath said chair; c. a column upstanding from said platform supporting said X-ray source and X-ray film holder, said column being rotatable about a vertical axis of rotation while being transported through said closed path of travel by said platform such that said X-ray source and X-ray film holder are orbited about the head of a patient through an orbital path which parallels the shape of the dental arch; and d. X-Y drive means carried by said platform and cooperating with said base for moving said platform with respect to said base through said closed path of travel, said X-Y drive means including a rotatable cam carried by said platform and a pair of reaction arms extending between said cam and base, each of said reaction arms being freely movable with respect to said base along one axis thereof and fixed with respect to said base along another axis thereof, the throw of said cam during the rotation thereof forcing said reaction arms to move said cam and therefore said platform with respect to said base through said closed path of travel.
 15. X-ray apparatus as set forth in claim 14 wherein said cam is disc-shaped having an endless cam groove in both the top and bottom surfaces thereof defining respectively the X and Y components of motion of said platform, and each of said reaction arms being associated with a cam follower engaged in one of said cam grooves.
 16. X-ray apparatus as in claim 15 including a vertical shaft depending from said platform, said X-Y drive means including: a. a pick-off arm having one end journaled to said shaft, one of said cam followers being fixed to said arm; b. a lead screw and nut on said pick-off arm, said screw being rotated for driving said nut along said pick-off arm towards and away from said shaft; and c. one of said reaction arms being journaled at one end of said nut, the movement of said nut towards and away from said shaft acting to decrease and increase respectively the throw of said cam.
 17. X-ray apparatus as in claim 15 including a vertical shaft depending from said platform, said X-Y drive means including: a. an L-shaped pick-off arm journaled intermediate its ends to said shaft, one of said cam followers being fixed on one leg of said L-shaped pick-off arm; b. a led screw and nut on said second leg of said L-shaped pick-off arm, the rotation of said led screw driving said nut along said leg towards and away from said shaft; c. a pin on said nut; and d. means including one of said reaction arms journaled to said pin, the movement of said nut towards and away from said shaft acting to decrease and increase respectively the throw of said cam.
 18. Dental X-ray apparatus of the type for taking a full mouth X-ray comprising: a. a base adapted to rest on a floor surface; b. a patient support means on said base including means for holding the head of a patient at a reference point; c. a platform supported on said base for movement relative to said base through a closed path of travel in an X-Y plane beneath said patient support means; d. an X-ray source and film holder, said source and film holder being spaced and in line and rotatable aBout a vertical axis upstanding from said platform so as to orbit the head of a patient held at said reference point; e. means for moving said platform through said closed path of travel while rotating said X-ray source and film holder about said vertical axis, the rotational movement of said X-ray source and film holder together with the movement of said vertical axis producing a net movement of said X-ray source and film holder along a path of travel which parallels the dental arch of a patient''s head held at said reference point; f. means for symmetrically changing the size of said closed path of travel; and g. means for translating said platform towards and away from said reference point as the size of said path of travel is respectively decrease and increased. 